Electrical motors are in vast use and impact every aspect of industrial, commercial and residential life. Such motors can vary from small, fractional motors that can be found, for example, in washing machines and refrigerators, to large industrial applications for driving manufacturing equipment, fans and the like. Motors are commonly used to convert electrical energy into rotating energy or rotational force.
Typically, a motor includes a rotating central portion referred to as a rotor and a stationary outer portion referred to as a stator. The stator and rotor are housed in a housing that contains the motor. Both the rotor and stator contain electrical conducting elements. Rotor and stator cores can be formed with varying numbers of slots, which are the openings that receive the electrical conducting elements.
A rotor core is the central portion of the rotor that contains the conductive elements. The number of bars in rotor cores can vary considerably. In smaller, fractional squirrel-cage motors, for example, those having rotor diameters of about two inches, the number of bars is generally between 8 and 52.
The core structure is typically formed as a plurality of stacked plates or laminations. The laminations, which can be metal, may be punched in a press and subsequently stacked one on top of another to form the core. In some cores, the laminations are rotated relative to one another to account for possible asymmetries in the lamination material. In other, non-rotated cores, the laminations can merely be stacked one on top of another and interlocked with one another to form a rigid core structure, and to prevent the laminations from shifting relative to one another.
In one known interlocking arrangement, each lamination has a dimple or recess punched into the surface, which forms a corresponding projection on the opposite side of the lamination. The laminations are then stacked one on top of the other with the projections from one lamination engaging and resting in the recess in the next adjacent lamination. In this nested arrangement, the laminations are kept in alignment with one another by engagement of the projections and recesses. This is a common and accepted method for interlocking laminations.
Although such known methods are in common practice, they do have their drawbacks. First, this direct nested arrangement provides a relatively short path and thus, a low impedance current path for eddy currents. This, as will be recognized by those skilled in the art, can result in increased electromagnetic losses through the core. This arrangement decreases the efficiency of the motor from which the stator core is constructed.
Accordingly, there continues to be a need for a rotor core lamination interlocking arrangement that readily facilitates manufacture of laminations and rotor cores therefrom which interlocking arrangement creates a high impedance current path for eddy currents to reduce the electromagnetic losses through the rotor.